Neurofibromatosis type I (NF1), a common dominant condition, is characterized by abnormal proliferation of neural crest derived cells, including Schwann cells (thought to be the clonal element) in neurofibromas. The current therapy for neurofibromas is surgery, which is usually insufficient. Neurofibromas are often aggravated during puberty and pregnancy, suggesting an altered sensitivity to steroid hormones. NF1 patients and their physicians worry about this possible correlation when faced with decisions about hormone therapies for birth control, menopause, or disease treatments. To investigate this hypothesis, the type, relative quantity and localization of hormone receptors present in NF1 tumor Schwann cell cultures compared to normal Schwann cells will be measured through RT-PCR/Western blot and immunofluorescence, respectively. To investigate the functional role of these receptors, the tumor cultures will be assayed for increased proliferation and/or survival in response to these hormones. Expression of genes believed to be downstream targets of steroid hormones will also be analyzed. These studies will characterize the role of hormones in neurofibroma development, allowing for more educated medical decisions, as well as identifying potential targets for inhibiting tumor development.